1. Field of the Invention
This invention relates to a bonding structure of an electronic device and a method for manufacturing the same.
2. Description of the Related Art
IC units manufactured by TAB (Tape Automated Bonding) method have been known, in which the IC chip is bonded to metal lead foil adhered onto an upper surface of a resin film (carrier film). These IC units are used, for example, for electrically connecting a liquid crystal display panel to a printed circuit board and the like in table-top electronic computers. The IC chip which is used to connect the liquid crystal display panel and the printed circuit board serves for driving the liquid crystal device.
When the IC unit is used to electrically connect the liquid crystal display panel and the printed circuit board, the IC unit is required to ensure a steadfast connecting between the above components during a mounting work. Therefore, the IC-chip leads must be firmly bonded to the connecting leads of the liquid crystal display panel and the printed circuit board so that the IC-chip leads do not separate from the above connecting leads.
For ensuring the firm bonding of the IC-chip leads, one of the conventional technique is shown in Japanese patent unexamined disclosure 57-1250, which discloses that, in the bonding method of this type, the IC-chip leads extended from the IC-chip body are bent slightly down at its free end portions and these bent portions are further bent forward, thereby the extending leads being bent into a dull steplike shape. The bent portions of the IC chip leads are arranged on the connecting leads of the liquid crystal display panel and the printed circuit board, respectively solder is applied between the free ends of IC-chip leads and the above mentioned connecting leads to provide a solder pool between them, thereby ensuring the firm bonding between them enough for preventing the IC-chip leads from separating from the connecting leads.
The conventional technique mentioned above can not be suitably used in a structure where the extremely fine pitches and the narrow widths for the metal leads are required In such case, for preventing excess solder from flowing into the spaces between leads so as to make a short circuit, solder must be applied as little as possible while ensuring a high bonding strength. To achieve a firm soldering with a bit of solder, the amount of solder to be provided to each of metal leads must be measured with a high accuracy. When a bit of solder is provided for bonding, one solder pool is not enough for ensuring a firm bonding strength Further, each of metal leads must be as thin as possible just as foil. In this structure, however the metal leads are too flexible so that the free ends of the leads might be steady. Therefore, in the conventional method, another problem is that it is very hard to position the free ends of the metal leads in the right place.